Question 1

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

Accepted Answer

DNA polymerase III is the enzyme that catalyzes the elongation of a DNA strand in the 5' → 3' direction during DNA replication. Primase synthesizes short RNA primers to initiate DNA synthesis, DNA ligase seals the nicks in the sugar-phosphate backbone of DNA, topoisomerase changes the topology of DNA by breaking and rejoining the DNA strands, and helicase unwinds the DNA double helix. However, none of these enzymes are responsible for the actual elongation of the DNA strand in the 5' → 3' direction.

Question 2

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism.Approximately what percentage of the nucleotides in this sample will be thymine?

Accepted Answer

A

Question 3

Which of the following investigator(s)was/were responsible for the following discovery?
In DNA from any species,the amount of adenine equals the amount of thymine,and the amount of guanine equals the amount of cytosine.

Accepted Answer

This discovery is known as Chargaff's rule, which was established by Erwin Chargaff in the 1950s through his analysis of DNA composition in various species.

Question 4

What is meant by the description "antiparallel" regarding the strands that make up DNA?

Accepted Answer

Antiparallel refers to the opposite directionality of the two strands that make up the DNA double helix. One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction. This results in the two strands being oriented in opposite directions, or antiparallel.

Question 5

To repair a thymine dimer by nucleotide excision repair,in which order do the necessary enzymes act?

Accepted Answer

Nucleotide excision repair involves the removal of a segment of nucleotides, including the damaged region, by an endonuclease. DNA polymerase I then fills in the gap left by the excised nucleotides, and DNA ligase seals the nick in the sugar-phosphate backbone. Therefore, the correct order is endonuclease, DNA polymerase I, and DNA ligase.

Question 6

One major difference in prokaryote replication versus eukaryote replication is

Accepted Answer

Prokaryotic chromosomes have a single origin of replication, meaning replication proceeds bidirectionally from one point, whereas eukaryotic chromosomes have multiple origins of replication, allowing for faster replication. The other choices are not accurate differences between prokaryotic and eukaryotic replication.

Question 7

Suppose you are provided with an actively dividing culture of E.coli bacteria to which radioactive thymine has been added.What would happen if a cell replicates once in the presence of this radioactive base?

Accepted Answer

During DNA replication, the two strands of DNA separate, and each strand serves as a template for the synthesis of a new complementary strand. In the presence of radioactive thymine, the newly synthesized DNA strands will incorporate the radioactive thymine, resulting in both daughter cells having radioactive DNA. Option A is incorrect because both daughter cells will have radioactive DNA. Option B is incorrect because at least one of the daughter cells should have radioactive DNA. Option C is incorrect because only thymine would be radioactive, not all four bases. Option D is incorrect because radioactive thymine would pair with radioactive adenine, not non-radioactive guanine.

Question 8

Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA?

Accepted Answer

The diameter of the helix can be directly determined from X-ray diffraction photographs of crystallized DNA. Other options listed require additional analysis and techniques to determine.

Question 9

In his transformation experiments,what did Griffith observe?

Accepted Answer

Griffith observed that when he mixed a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain, some of the living cells were transformed into the pathogenic form. This was the first evidence of bacterial transformation, which led to the discovery of DNA as the genetic material.

Question 10

At a specific area of a chromosome,the sequence of nucleotides below is present where the chain opens to form a replication fork:
3' C C T A G G C T G C A A T C C 5'
An RNA primer is formed starting at the underlined T (T)of the template.Which of the following represents the primer sequence?

Accepted Answer

RNA primers are synthesized using the DNA template strand, and they are complementary and antiparallel to the template. The correct sequence must replace thymine (T) with uracil (U) because RNA contains uracil instead of thymine. Therefore, the correct sequence starting from the underlined T and going in the 5' to 3' direction (opposite to the 3' to 5' direction of the template strand) is 5' A C G U U A G G 3'.

Question 11

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

Accepted Answer

The sequence of bases (adenine, guanine, cytosine, and thymine) in DNA determines the genetic information encoded in the molecule. The other options listed are important components of DNA structure, but do not directly contribute to the information stored in the molecule.

Question 12

How do we describe transformation in bacteria?

Accepted Answer

Transformation in bacteria refers to the process by which bacteria take up external DNA and incorporate it into their own genome. This can occur naturally or artificially through various techniques such as electroporation or bacterial conjugation. Choice A refers to reverse transcription, not transformation. Choice B refers to transcription, not transformation. Choice C describes the infection of cells by a virus, not bacteria. Choice D refers to DNA replication, not transformation.

Question 13

The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes.What does this most probably reflect?

Accepted Answer

The high conservation of telomere DNA throughout evolution suggests that the critical function of telomeres, which is to protect the ends of chromosomes and maintain genome stability, must be maintained. Conserved DNA sequences are usually functionally important, as they are under selective pressure to remain unchanged over time.

Question 14

In trying to determine whether DNA or protein is the genetic material,Hershey and Chase made use of which of the following facts?

Accepted Answer

Hershey and Chase made use of the fact that DNA contains phosphorus in its backbone, while proteins do not. They labeled the DNA and protein of bacteriophages with radioactive isotopes of phosphorus and sulfur, respectively, and then allowed the phages to infect bacteria. They found that only the radioactive phosphorus from the DNA entered the bacterial cells, indicating that DNA was the genetic material.

Question 15

After mixing a heat-killed,phosphorescent strain of bacteria with a living nonphosphorescent strain,you discover that some of the living cells are now phosphorescent.Which observations would provide the best evidence that the ability to fluoresce is a heritable trait?

Accepted Answer

Descendants of the living cells being phosphorescent is the best evidence that the ability to fluoresce is a heritable trait, as it suggests that the genetic information responsible for the phosphorescence has been passed down from generation to generation. The other choices (A, B, C, and E) all involve some form of material being passed from the heat-killed strain to the living strain, but do not necessarily imply that the trait is heritable.

Question 16

Eukaryotic telomeres replicate differently than the rest of the chromosome.This is a consequence of which of the following?

Accepted Answer

The answer of Eukaryotic telomeres replicate differently than the rest...

Question 17

The enzyme telomerase solves the problem of replication at the ends of linear chromosomes by which method?

Accepted Answer

Telomerase adds numerous short DNA sequences, specifically TTAGGG, to the ends of chromosomes. These telomere sequences protect the important genetic information from being lost during replication and prevent the ends of chromosomes from being mistaken as double-strand breaks that could cause the cell to undergo DNA repair mechanisms or apoptosis.

Question 18

In E.coli,there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin.Which of the following would you expect as a result of this mutation?

Accepted Answer

The helicase enzyme is responsible for unwinding the double-stranded DNA at the origin of replication, creating a replication fork. Without functional helicase, replication cannot proceed and no replication fork will be formed. Therefore, option B is the best choice. Options A, C, D, and E are not related to the role of helicase in replication.

Question 19

In an analysis of the nucleotide composition of DNA,which of the following will be found?

Accepted Answer

In DNA, the number of adenine (A) nucleotides is always equal to the number of thymine (T) nucleotides, and the number of cytosine (C) nucleotides is always equal to the number of guanine (G) nucleotides. This means that A + C = G + T, which is the only choice that reflects this parity in nucleotide composition. A = C (Option A) and A = G and C = T (Option B) are incorrect because they do not reflect the equal amounts of all four nucleotides present in DNA. G + C = T + A (Option D) is also incorrect because it incorrectly suggests that guanine (G) and cytosine (C) always pair with thymine (T) and adenine (A), respectively, which is not true.

Question 20

An Okazaki fragment has which of the following arrangements?

Accepted Answer

An Okazaki fragment is a short fragment of DNA that is synthesized on the lagging strand during DNA replication. These fragments are created in a series of steps: first, RNA primers are added by primase, then DNA polymerase III adds DNA nucleotides in the 5' to 3' direction. However, on the lagging strand, the overall direction of replication is from 3' to 5', so the polymerase has to add nucleotides in a backwards fashion, resulting in short, discontinuous fragments. These fragments are then joined together by DNA ligase. The arrangement of an Okazaki fragment is therefore 5' RNA nucleotides followed by DNA nucleotides in the 3' to 5' direction.

Quiz 16: The Molecular Basis of Inheritance